As for a nut for fixing an automobile wheel, a box nut is used in order to prevent entry of water, mud or the like or to improve the external appearance. This box nut has a bowl-shaped cap welded to the nut. The present invention belongs to the technical field that relates to the welding of such nut.
In the prior art, a cap and a nut are abutted together and in this state they are held by a chuck, and with the cap and nut integrally held standby on the axis between both electrodes, the latter advance to press the cap and nut and a welding current is passed to complete the welding. Particularly, electric resistance welding is performed by holding a nut on the flat end surface of the fixed electrode by a chuck, fitting thereon a cap held also by a chuck, and advancing the movable electrode into this state. Such system is disclosed in FIG. 3 of Japanese Unexamined Patent Publication Hei9-85464.
With the prior art described above, since the cap and nut, which are not welded together, are held by the chuck, iron scraps from somewhere or the like entering the holding dogs of the chuck causes a misalignment in the relative position between the cap and nut, resulting in the two parts being welded in the deviated state. Since the cap and nut held by the chuck are kept standby and the electrodes are advanced thereto, even the slightest misalignment in the relative position between the electrodes, cap and nut leads to the failure of the cap and nut to be correctly held by the electrodes, so that the cap and nut are nonalignedly welded or the cap is driven out when abutted against the nut. Further, with the chuck system, it is necessary to greatly increase the precision of the chuck mechanism, requiring that a correspondingly high installation be prepared. As the number of parts handled by the chuck mechanism increases, the movable parts, such as jaws and shaft, wear, incurring a lowering in operating precision.
According to an embodiment of the present invention, a box nut welding method is characterized in that one electrode is provided with a recess for receiving and holding a bowl-shaped cap and the other electrode is provided with a recess for receiving and holding a nut, the arrangement being such that the open end of the cap and the end surface of the nut held by the respective electrodes are pressed against each other by the advance of the electrode, whereupon a welding current is passed, thereby welding the cap and nut. Since the cap and nut are respectively held in the recesses of the electrodes, both parts assume the correct relative position when both electrodes on the same axis approach each other to abut both parts against each other; thus, a box nut of satisfactory welding precision is obtained. Since the cap and nut are received in the recesses of the electrodes, the relative position between the electrodes and the parts held therein can be accurately set, so that welded parts of high precision as described above can be obtained. Further, since the cap and nut are held directly by the electrodes, the need for employing a chuck mechanism as used in the prior art is eliminated, freeing the operator from the foregoing problems caused by the use of a chuck.
The cap and nut are moved axially of the electrodes after their axes may be positioned coaxial with the axis of the electrodes, and then they are received and held in the recesses of the electrodes. That is, the loci of the cap and nut are moved to the recesses of the electrodes after the cap and nut are coaxial with the axis of the electrodes, so that the loci of both parts assume the simplest form; therefore, the process for holding the parts in the electrodes is simply and reliably effected, ensuring that reliable operation is attained.
The cap and nut may reach the recesses of the electrodes as they are held by respective feed members that perform square motions. Both parts reach the recesses of the electrodes as they are held by the feed members, in which case the loci of the feed members are provided by square motions, thus making it easier to attain a reliable operation including movement of both parts to the electrode recesses after both parts are positioned on the electrode axis. That is, it is required that the feed members provide a locus for returning to the parts-receiving position and a locus for moving to the advance-ready position after parts have been received. These requirements are reliably achieved by the square motions.
A guide pin adapted to fit into the threaded hole in the nut may be installed in the recess of the nut holding electrode. As for the holding of the nut by the electrode, installing such guide pin can prevent the nut from abnormally tilting during pressing for welding, so that correct abutment of the nut against the cap is ensured. As for the cap, if the cap is bowl-shaped, the cap is pressed against the nut end surface with the uniformity of entire open end of the cap during pressing against the nut in a manner analogous to a phenomenon in which a ball freely rolls in the electrode recess. That is, the cap has a self-aligning action imparted thereto.
According to another embodiment of the invention, a box nut welding device is characterized in that one electrode is provided with a recess for receiving and holding a bowl-shaped cap and the other electrode is provided with a recess for receiving and holding a nut, both electrodes being disposed on the same axis, the device having a cap feeding mechanism for carrying the cap to the recess of the electrode subsequent to the positioning of the cap coaxial with the electrode axis, and a nut feeding mechanism for carrying the nut to the recess of the electrode subsequent to the positioning of the nut coaxial with the electrode axis. Since the cap and nut are respectively held in the recesses of the electrodes, both parts assume the correct relative position when both electrodes on the same axis approach each other to abut both parts against each other; thus, a box nut of satisfactory welding precision is obtained. Since the cap and nut are received in the recesses of the electrodes, the relative position between the electrodes and the parts held therein can be accurately set, so that welded parts of high precision as described above can be obtained. Further, since the cap and nut are held directly by the electrodes, the need for employing a chuck mechanism as used in the prior art is eliminated, freeing the operator from the problems caused by the use of a chuck.
Driving means may be combined so that the feed members of the cap feeding mechanism and nut feeding mechanism perform square motions. Both parts reach the recesses of the electrodes as they are held by the feed members, in which case the loci of the feed members are provided by square motions, thus making it easier to attain a reliable operation including movement of both parts to the electrode recesses after both parts are positioned on the electrode axis. That is, it is required that the feed members provide a locus for returning to the parts-receiving position and a locus for moving to the advance-ready position after parts have been received. These requirements are reliably achieved by the square motions.
A guide pin adapted to fit into the threaded hole in the nut may be installed in the recess of the nut holding electrode, the guide pin having a means for allowing the box nut to escape from the electrode recess after welding. As for the holding of the nut by the electrode, installing such guide pin can prevent the nut from abnormally tilting during pressing for welding, so that correct abutment of the nut against the cap is ensured. Where the guide pin is provided with an escape means, such as a compressed air spout or a push-out rod, the completed box nut is allowed to escape from the electrode. Particularly, since the cap is internally acted on by an escape force, the force necessary for escape is reliably transmitted to the box nut and the reliability of escape itself is increased. As for the cap, if the cap is bowl-shaped, the cap is pressed against the nut end surface with the uniformity of entire open end of the cap during pressing against the nut in a manner analogous to a phenomenon in which a ball freely rolls in the electrode recess. That is, the cap has a self-aligning action imparted thereto.
According to still other embodiment of the invention, a box nut welding device is characterized in that one electrode is provided with a recess for receiving and holding a bowl-shaped cap and the other electrode is provided with a recess for receiving and holding a nut, both electrodes being disposed on the same axis, the device having a cap feeding mechanism for carrying the cap to the recess of the electrode subsequent to the positioning of the cap coaxial with the electrode axis, and a nut feeding mechanism for carrying the nut to the recess of the electrode by a feed rod advancing in a direction inclined with respect to the axis of the electrode. Since the cap and nut are respectively held in the recesses of the electrodes, both parts assume the correct relative position when both electrodes on the same axis approach each other to abut both parts against each other; thus, a box nut of satisfactory welding precision is obtained. Since the cap and nut are received in the recesses of the electrodes, the relative position between the electrodes and the parts held therein can be accurately set, so that welded parts of high precision as described above can be obtained. Further, since the cap and nut are held directly by the electrodes, the need for employing a chuck mechanism as used in the prior art is eliminated, freeing the operator from said problems caused by the use of a chuck. Further, since the nut is fed to the electrode recess by the feed rod advancing in an inclined direction, it becomes possible to bring the nut to the electrode from a remote place, a fact that is convenient when the space around the electrode is limited.
According to still other embodiment of the invention, a box nut welding device is characterized in that one electrode is provided with a recess for receiving and holding a bowl-shaped cap and the other electrode is provided with a recess for receiving and holding a nut, both electrodes being disposed on the same axis, the device having a cap feeding mechanism for carrying the cap to the recess of the electrode subsequent to the positioning of the cap coaxial with the electrode axis, and a nut feeding mechanism for carrying the nut to the recess of the electrode subsequent to the positioning of the nut coaxial with the electrode axis, the feed member of the cap feeding mechanism for holding the cap and the feed member of the nut feeding mechanism for holding the nut having a relative position such that when both feed members are advanced, they do not interfere with each other. Since the cap and nut are respectively held in the recesses of the electrodes, both parts assume the correct relative position when both electrodes on the same axis approach each other to abut both parts against each other; thus, a box nut of satisfactory welding precision is obtained. Since the cap and nut are received in the recesses of the electrodes, the relative position between the electrodes and the parts held therein can be accurately set, so that welded parts of high precision as described above can be obtained. Further, since the cap and nut are held directly by the electrodes, the need for employing a chuck mechanism as used in the prior art is eliminated, freeing the operator from said problems caused by the use of a chuck. With the chuck mechanism, if an iron scrap or the like is present between the chuck dog and the part, the part is held in its inclined state, so that correct welding is sometimes unattainable. Further, the feed member of the cap feeding mechanism and the feed member of the nut feeding mechanism are in positional relation such that they do not interfere with each other when they are advanced. This results in the cap feeding mechanism and the nut feeding mechanism being concentrated in an area as close to the electrode axis as possible since both feed members are allowed to advance between both electrodes, a fact that is very advantageous for minimizing the space for the entire welding device. And since both feed members are allowed to simultaneously advance between the electrodes, the holding of the cap and nut in the electrodes can be efficiently effected in a short time.
The advancing and retracting directions of the feed member of the cap feeding mechanism and the advancing and retracting directions of the feed member of the nut feeding mechanism may be opposed to each other in a straight line as seen in the direction of the electrode axis or cross each other. This allows both feed members to advance and retract without interfering with each other, as described above, so that space minimization and short-time feeding are made possible. Further, when the advance and retraction axes of both feed members cross each other as described above, the cap feeding mechanism and the nut feeding mechanism can be brought close to each other and concentrated, a fact that is further advantageous in respect of space.
Alternatively, a box nut welding device is characterized in that one electrode is provided with a recess for receiving and holding a bowl-shaped cap and the other electrode is provided with a recess for receiving and holding a nut, both electrodes being disposed on the same axis, both electrodes being disposed on the same axis, the device having a cap feeding mechanism for carrying the cap to the recess of the electrode subsequent to the positioning of the cap coaxial with the electrode axis, and a nut feeding mechanism for carrying the nut to the recess of the electrode subsequent to the positioning of the nut coaxial with the electrode axis, the feed member of the cap feeding mechanism for holding the cap and the feed member of the nut feeding mechanism for holding the nut having a relative position such that when both feed members are advanced toward the electrode axis, they do not interfere with each other, the advancing and retracting directions of the feed member of the cap feeding mechanism and the advancing and retracting directions of the feed member of the nut feeding mechanism being opposed to each other as seen in the direction of the electrode axis or crossing each other.
According to still other embodiment of the invention, a box nut welding device is characterized by comprising a movable electrode and a fixed electrode that are disposed coaxial with a vertical axis, the fixed electrode being formed with a recess for holding a nut, a feed member adapted to advance and retract in a direction substantially at right angles with the axis while holding a cap, the feed member being constructed to move vertically along the axis, the arrangement being such that with a cap mounted on the nut held by the fixed electrode, the movable electrode is lowered to effect pressing and passage of current.
The advance of the feed member stops where the axis of the cap held by the feed member coincides with the axis of the electrode, and then the feed member moves along the axis of the electrode and the open end of the cap is mounted on the end surface of the nut. Then the movable electrode advances to press the cap against the nut and passes a current therethrough to complete welding. After completion, the box nut is removed from the recess of the fixed electrode. In addition, the feed member executes a so-called square motion comprising advancing movement toward the electrode axis, downward movement along the electrode axis, retracting movement, and upward movement. Thus, an accurate and highly durable device is provided by employing not a means unstable in terms of precision, such as a chuck, and but a simple action comprising a combination of advance and retraction of the feed member and its movement in the direction of the axis of the electrodes. The fixed electrode is formed with a recess and the nut held therein is on standby with good stability. Since the system is such that the cap is mounted on the standby nut, positional deviation of the cap never takes place. Further, since the behavior imparted to the cap is simple as described above, he mechanism employed herein is simplified and saves much installation space.
When the feed member for caps is formed with a cap receiving chamber, the cap is held in the receiving chamber and reliably moved as described above. Further, since the cap movement is effected with the cap put in the receiving chamber, even if interference with an adjacent member should occur during movement, the cap remains in its protected state, never accidentally falling off.
The receiving chamber may be opened in the lower side and may be formed with an inlet opposed to and communicating with a cap feed chute and an outlet through which a cap relatively goes out of the receiving chamber, the receiving chamber having installed therein an attracting means for holding a cap. Since the inlet and outlet for the cap into and from the receiving chamber are thus formed and since the lower side of the receiving chamber is opened, introduction of the cap into the receiving chamber, the mounting of the cap on the nut, and retraction of the feed member with the cap remaining therein are reliably realized.
The open end of a cap may fit in an annular groove formed in the end surface of a nut. Such fitting in the groove ensures that the mounting of the cap on the end surface of the nut is realized with high stability.